Tissue treatment system and method for tissue perfusion using feedback control

ABSTRACT

A system, ablation probe, and method is provided for treating tissue, e.g., tissue having tumors. The treatment system is configured to automatically deliver infusaid to tissue when needed and comprises an ablation probe having an ablative element and at least one perfusion exit port. The system further comprises an ablation source operably coupled to the ablative element, and a pump assembly operably coupled to the perfusion exit port(s). The pump assembly is configured for pumping infusaid out through the perfusion exit port(s), preferably during the ablation process. The system further comprises a feedback device configured for controlling the amount of infusaid displaced by the pump assembly based on a sensed tissue parameter, e.g., tissue temperature or tissue impedance.

RELATED APPLICATIONS

This application is a continuation of, and claims the benefit of andpriority to, U.S. application Ser. No. 12/037,882, filed on Feb. 26,2008, now U.S. Pat. No. 9,757,188, which claims the benefit of andpriority to U.S. application Ser. No. 10/740,692, now U.S. Pat. No.7,347,859, filed on Dec. 18, 2003, the disclosure of each of which areincorporated in their entirety for all purposes.

FIELD OF INVENTION

The invention(s) herein relate generally to the structure and use ofradio frequency (RF) electrosurgical probes for the treatment of tissue.

BACKGROUND

The delivery of radio frequency (RF) energy to target regions withinsolid tissue is known for a variety of purposes of particular interestto the present invention(s). In one particular application, RF energymay be delivered to diseased regions (e.g., tumors) for the purpose ofablating predictable volumes of tissue with minimal patient trauma. RFablation of tumors is currently performed using one of two coretechnologies.

The first technology uses a single needle electrode, which when attachedto a RF generator, emits RF energy from the exposed, non-insulatedportion of the electrode. This energy translates into ion agitation,which is converted into heat and induces cellular death via coagulationnecrosis. The second technology utilizes multiple needle electrodes,which have been designed for the treatment and necrosis of tumors in theliver and other solid tissues. In general, a multiple electrode arraycreates a larger lesion than that created by a single needle electrode.

In theory, RF ablation can be used to sculpt precisely the volume ofnecrosis to match the extent of the tumor. By varying the power outputand the type of electrical waveform, it is possible to control theextent of heating, and thus, the resulting ablation. However, the sizeof tissue coagulation created from a single electrode, and to a lesserextent a multiple electrode array, has been limited by heat dispersion.As a result, multiple probe insertions must typically be performed inorder to ablate the entire tumor. This process considerably increasestreatment duration and patent discomfort and requires significant skillfor meticulous precision of probe placement. In response to this, themarketplace has attempted to create larger lesions with a single probeinsertion. Increasing generator output, however, has been generallyunsuccessful for increasing lesion diameter, because an increasedwattage is associated with a local increase of temperature to more than100° C., which induces tissue vaporization and charring. This thenincreases local tissue impedance, limiting RF deposition, and thereforeheat diffusion and associated coagulation necrosis. In addition, patienttolerance appears to be at the maximum using currently available 200 Wgenerators.

It has been shown that the introduction of saline into targeted tissueincreases the tissue conductivity, thereby creating a larger lesionsize. This can be accomplished by injecting the saline into the targetedtissue with a separate syringe. This injection can take place prior toor during the ablation process. See, e.g., Goldberg et al.,Saline-Enhanced Radio-Frequency Tissue Ablation in the Treatment ofLiver Metastases, Radiology, January 1997, pages 205-210. It has alsobeen shown that, during an ablation procedure, the ablation probe,itself, can be used to perfuse saline (whether actively cooled or not)in order to reduce the local temperature of the tissue, therebyminimizing tissue vaporization and charring. For example, some probesmay allow a physician, either before or during the ablation process, tomanually inject a specific amount of fluid through the probe, whichperfuses out of the needle electrode. These manually performed perfusionprocesses, however, are imprecise in that the optimum amount ofperfusion is difficult to achieve. These perfusion processes also eitherdemand additional attention from the physician performing the ablationprocedure or require additional personnel to ensure that enough salineis perfused into the tissue.

One probe, which uses a multiple needle electrode array, can beconnected to an injection pump network comprised of several syringesconnected in parallel. The syringes are designed to automaticallydeliver the fluid through the probe and out of the respective needleelectrodes, presumably at a prescribed time during the ablation process.While this automated perfusion process does not demand additionalattention from the physician, it is imprecise and does not providedynamic control over the amount of saline perfused into the targettissue, as well as the timing of the saline perfusion.

In addition, when needle electrodes are used to perfuse saline into thetarget tissue, whether performed manually or automatically, theperfusion exit ports within the needle electrodes often clog as theneedle electrodes are introduced through the tissue. As a result,perfusion of the saline is hindered, and thus, the amount of salineperfused into the tissue may be insufficient. Even if the perfusion exitports within the needle electrode(s) are not clogged, the amount ofsaline delivered through the needle electrode(s) may be insufficient dueto an insufficient number or size of the perfusion exit ports. Also, inthe automated perfusion process, additional time and skill is requiredto set up and connect the pump assembly to the ablation probe, therebyincreasing the complexity of the ablation procedure.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention(s), a tissue treatmentsystem is provided, which comprises an ablation probe. In oneembodiment, the ablation probe is rigid, so that it can bepercutaneously or laparoscopically introduced into a patient's body.Alternatively, the ablation probe can be flexible, e.g., if the ablationprobe takes the form of an intravascular or extravascular catheter. Theablation probe further comprises an ablative element. Although manytypes of ablative elements are contemplated, the ablative elementpreferably takes the form of electrode(s), e.g., a single needleelectrode or an array of needle electrodes. The ablation probe furthercomprises at least one perfusion exit port, which can be used to perfusean infusaid into the surrounding tissue.

The system further comprises an ablation source operably coupled to theablative element. If the ablative element is an electrode, the ablationsource can be a RF generator. The system further comprises a pumpassembly operably coupled to the perfusion exit port(s). The pumpassembly can be external to the ablation probe or can be carried by theablation probe. In one embodiment, the system comprises a source ofinfusaid, in which case, the pump assembly is configured for pumping theinfusaid from the infusaid source out through the perfusion exitport(s).

The system further comprises a feedback device configured forcontrolling the amount of infusaid displaced by the pump assembly basedon a sensed tissue parameter, e.g., tissue temperature or tissueimpedance. In one embodiment, the feedback device comprises a sensorconfigured for sensing the tissue parameter, and a perfusion controllercoupled to the sensor and the pump assembly. The perfusion controller isconfigured for controlling the pump assembly based on the sensed tissueparameter. In another embodiment, the feedback device comprises aperfusion valve associated with the distal end of the shaft. In thiscase, the perfusion valve forms the perfusion exit port, wherein theperfusion valve changes the size of the perfusion exit port based on thesensed tissue parameter. Thus, it can be appreciated that the treatmentsystem automatically delivers infusaid to the tissue when needed.

In accordance with another aspect of the invention(s), a method oftreating tissue is provided. The method comprises ablating the tissue(e.g., using radio frequency energy), sensing a tissue parameter (e.g.,tissue temperature and/or tissue impedance), and perfusing the tissuewith an infusaid based on the sensed tissue parameter. The tissue can beperfusing at anytime relative to the ablation process, but in apreferred method, the tissue is perfused during the tissue ablation. Ifthe sensed tissue parameter is tissue temperature, the tissue perfusionmay be commenced when the sensed temperature surpasses a firsttemperature, and ceased when the sensed temperature drops below a secondtemperature threshold. In a similar manner, if the sensed tissueparameter is tissue impedance, the tissue perfusion may be commencedwhen the sensed impedance surpasses a first impedance threshold, andceased when the sensed impedance drops below a second impedancethreshold.

In accordance with an aspect of the invention(s), an ablation probecomprises an elongate shaft having a distal end, and an ablative elementdisposed on the distal end of the shaft. In one embodiment, the ablationprobe is rigid, so that it can be percutaneously or laparoscopicallyintroduced into a patient's body. Alternatively, the ablation probe canbe flexible, e.g., if the ablation probe takes the form of anintravascular or extravascular catheter. Although many types of ablativeelements are contemplated, the ablative element preferably takes theform of electrode(s), e.g., a single needle electrode or an array ofneedle electrodes. The ablation probe further comprises at least oneperfusion exit port, which can be used to perfuse an infusaid into thesurrounding tissue. The ablation probe further comprises a perfusionlumen longitudinally extending within the shaft, and a perfusion controlvalve associated with the distal end of the shaft. The perfusion controlvalve has a port, the size of which changes with temperature. In oneembodiment, the perfusion control valve comprises a reed valve having atleast one reed, e.g., a pair of opposing reeds, or even four reeds. Thereeds are configured change shape in order to control the size of theport. For example, each reed can comprise a bi-metallic flange or anitinol flange that bends in the presence of a temperature change.

In accordance with an aspect of the invention(s), an ablation probecomprises an elongated shaft, which is preferably sufficiently rigid forpercutaneous or laparoscopic introduction into a patient's body.Alternatively, the probe shaft can be flexible, e.g., if the ablationprobe takes the form of an intravascular or extravascular catheter. Theablation probe further comprises an ablative element. Although manytypes of ablative elements are contemplated by the present invention(s),the ablative element preferably takes the form of electrode(s), e.g., asingle needle electrode or an array of needle electrodes.

The ablation probe further comprises a perfusion lumen that extendsthrough the probe shaft, and at least one perfusion exit port in fluidcommunication with the perfusion lumen. The perfusion lumen can be usedto deliver an infusaid to the perfusion exit port(s) for perfusion ofthe surrounding tissue. The perfusion exit port(s) can be configured inany manner, but in one embodiment, side ports are provided. Theperfusion exit port(s) can also be carried by the ablative element. Theablation probe further comprises a wicking material, e.g., cotton orfabric, disposed in the perfusion lumen. In this manner, the infusaidthat travels through the perfusion lumen can be controlled withoutregard to the size of the perfusion exit port(s). The wicking materialpreferably is disposed within the entire length of the perfusion lumento provide maximum control, but may also be disposed in only a portionof the perfusion lumen, depending on the amount of control required.

In accordance with another aspect of the present invention, a tissuetreatment system comprises an ablation probe including an elongate shafthaving a distal end, an ablative element disposed on the distal end ofthe shaft, a perfusion lumen longitudinally extending within the shaft,at least one perfusion exit port in fluid communication with theperfusion lumen, and a wicking material disposed in the perfusion lumen.The detailed features of the ablation probe can be similar to ablationprobe described above. The system further comprises an ablation sourceoperably coupled to the ablative element. If the ablative element is anelectrode, the ablation source can be a RF generator. The system furthercomprises a pump assembly configured for pumping infusaid from theinfusaid source through the perfusion lumen. The pump assembly can beexternal to the ablation probe or can be carried by the ablation probe.In one embodiment, the system comprises a source of infusaid, in whichcase, the pump assembly is configured for pumping the infusaid from theinfusaid source out through the perfusion exit port(s).

In accordance with an aspect of the invention(s), an ablation probecomprises an elongated shaft, which is sufficiently rigid forpercutaneous or laparoscopic introduction into a patient's body.Alternatively, the probe shaft can be flexible, e.g., if the ablationprobe takes the form of an intravascular or extravascular catheter. Theablation probe further comprises an ablative element. Although manytypes of ablative elements are contemplated, the ablative elementpreferably takes the form of electrode(s), e.g., a single needleelectrode or an array of needle electrodes.

The ablation probe further comprises a perfusion lumen that extendsthrough the probe shaft, and at least one perfusion exit port in fluidcommunication with the perfusion lumen. The perfusion lumen can be usedto deliver an infusaid to the perfusion exit port(s) for perfusion ofthe surrounding tissue. The perfusion exit port(s) can be configured inany manner, but in one embodiment, side ports are provided. Theperfusion exit port(s) can also be carried by the ablative element.

The ablation probe further comprises a pump assembly carried by theproximal end of the shaft. The pump assembly is configured for pumpinginfusaid through the perfusion lumen and out the perfusion exit port(s).In one embodiment, the pump assembly comprises a reservoir for storingthe infusaid, and a perfusion inlet port configured for transferringinfusaid from an external source into the reservoir. In this case, theablation probe further comprises a one-way check valve between theperfusion inlet port and the reservoir, wherein the check valve isconfigured for preventing the infusaid from being conveyed from thereservoir back through the perfusion inlet port. The ablation probe mayfurther comprise another one-way check valve between the perfusion lumenand the reservoir, wherein the other check valve is configured forpreventing the infusaid from being conveyed from the perfusion lumenback into the reservoir.

The pump assembly can be variously configured. In one embodiment, thepump assembly comprises a diaphragm adjacent the reservoir. In thiscase, the diaphragm has pumping stroke that displaces the infusaid fromthe reservoir into the perfusion lumen, and a return stroke thatdisplaces infusaid from an external source into the reservoir. Thediaphragm can have an active component, such as a piezoelectric element,configured for vibrating the diaphragm between pumping and returnstrokes. In another embodiment, the pump assembly comprises anelastomeric diaphragm adjacent the reservoir, wherein the diaphragm isconfigured for expanding to pressurize the reservoir in response to theconveyance of infusaid into the reservoir. In still another embodiment,the pump assembly comprises a plunger disposed in the reservoir and aspring configured to urge the plunger within the reservoir in onedirection to pressurize the reservoir. The plunger may further beconfigured to be displaced in another direction, e.g., by manuallypulling the plunger, to displace infusaid from an external source intothe reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of embodiments of theinvention, in which similar elements are referred to by common referencenumerals, and in which:

FIG. 1 is a plan view of a tissue treatment system constructed inaccordance with one embodiment of the invention(s);

FIG. 2 is a side view of a probe assembly used in the tissue treatmentsystem of FIG. 1;

FIG. 3 is a side view of a single-needle electrode ablation probe usedin the probe assembly of FIG. 2;

FIG. 4 is a side view of an alternatively single-needle electrodeablation probe that can be used in the probe assembly of FIG. 2;

FIG. 5 is a perspective view of a multi-needle electrode probe assemblythat can be used in the tissue treatment system of FIG. 1, wherein theprobe assembly is in its retracted state;

FIG. 6 is a perspective view of the probe assembly of FIG. 5, whereinthe probe assembly is in its deployed state;

FIGS. 7A-7C illustrate cross-sectional views of one method of using thetissue treatment system of FIG. 1 to treat tissue;

FIG. 8 is a side view of the proximal end of another ablation probe thatcarries a pump assembly for pumping infusaid through the ablation probe;

FIG. 9 is a cross-sectional view of the proximal end of the ablationprobe of FIG. 8, particularly showing the use of a piezoelectricactivated pump assembly;

FIG. 10 is a side view of the distal end of still another single-needleelectrode ablation probe that uses a perfusion control valve to regularthe flow of infusaid through the ablation probe, particularly showingthe perfusion control valve in a closed state;

FIG. 11 is an axial view of the ablation probe illustrated in FIG. 10;

FIG. 12 is a side view of the distal end of the ablation probe of FIG.10, wherein the perfusion control valve is particularly shown in an openstate;

FIG. 13 is an axial view of the ablation probe illustrated in FIG. 12;

FIG. 14 is a cross-sectional view of two reeds used in the perfusioncontrol valve illustrated in FIG. 12, taken along the lines 14-14;

FIG. 15 is a side view of a reed used in the perfusion control valve ofFIGS. 12 and 14, particularly showing the dynamic bending functionalityof the reed in response to temperature changes;

FIG. 16 is a cross-sectional view of the proximal end of still anotherablation probe that uses an elastomeric diaphragm pump assembly to pumpinfusaid through the ablation probe;

FIG. 17 is a cross-sectional view of the proximal end of yet anotherablation probe that uses a plunger to pump infusaid through the ablationprobe, particularly showing a plunger in its most distal position;

FIG. 18 is a cross-sectional view of the proximal end of the ablationprobe of FIG. 17, particularly showing the plunger in its most distalposition; and

FIG. 19 is a partially cutaway side view of the distal end of yetanother ablation probe that uses a wicking material to control the flowof infusaid through the ablation probe.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 illustrates a tissue treatment system 100 constructed inaccordance with an exemplary embodiment of the invention(s). The tissuetreatment system 100 generally comprises: a probe assembly 102configured for introduction into the body of a patient for ablativetreatment of target tissue; a radio frequency (RF) generator 104configured for supplying RF energy to the probe assembly 102 in acontrolled manner; a pump assembly 106 configured for perfusing aninfusaid, such as saline, out through the probe assembly 102, so that amore efficient and effective ablation treatment is effected; and aperfusion controller 107 configured for controlling the amount and/ortiming of the infusaid perfused out of the probe assembly 102.

Referring specifically now to FIG. 2, the probe assembly 102 generallycomprises an ablation probe 110 and a cannula 108 through which theablation probe 110 can be introduced. As will be described in furtherdetail below, the cannula 108 serves to deliver the active portion ofthe ablation probe 110 to the target tissue. The cannula 108 has aproximal end 112, a distal end 114, and a perfusion lumen 116 (shown inphantom) extending through the cannula 108 between the proximal end 112and the distal end 114. An open tapered point 118 is formed at thedistal end 114 of the cannula 108 in order to facilitate introduction ofthe cannula 108 through tissue. As will be described in further detailbelow, the cannula 108 may be rigid, semi-rigid, or flexible, dependingupon the designed means for introducing the cannula 108 to the targettissue. The cannula 108 is composed of a suitable material, such asplastic, metal or the like, and has a suitable length, typically in therange from 5 cm to 30 cm, preferably from 10 cm to 20 cm. If composed ofan electrically conductive material, the cannula 108 is preferablycovered with an insulative material. The cannula 108 has an outsidediameter consistent with its intended use, typically being from 1 mm to5 mm, usually from 1.3 mm to 4 mm. The cannula 108 has an inner diameterin the range from 0.7 mm to 4 mm, preferably from 1 mm to 3.5 mm.

Referring further to FIG. 3, the ablation probe 110 generally comprisesa shaft 120 having a proximal end 122 and a distal end 124, a singletissue penetrating needle electrode 126 formed at the end of the distalshaft end 124, and a perfusion lumen 128 (shown in phantom)longitudinally extending through the length of the probe shaft 120. Theprobe shaft 120 comprises a wall 130 that is preferably composed of anelectrically conductive material, such as stainless steel,nickel-titanium alloy, nickel-chromium alloy, spring steel alloy, andthe like. The needle electrode 126 is designed to penetrate into tissueas it is advanced to the target tissue site. Like the probe shaft 120,the needle electrode 126 is composed of an electrically conductivematerial, such as stainless steel, nickel-titanium alloy,nickel-chromium alloy, spring steel alloy, and the like. In fact, theneedle electrode 126 is preferably formed as a unibody structure withthe probe shaft 120.

In the illustrated embodiment, the needle electrode 126 has anopen-ended tapered tip similar to the tip 118 of the cannula 108. Theopen end is in fluid communication with the perfusion lumen 128, therebyproviding a perfusion exit port 129 from which infusaid is delivered tothe tissue. Alternatively or optionally, side ports (not shown) can beprovided in the probe shaft 120 in fluid communication with theperfusion lumen 128. Alternatively, the probe shaft 120 and/or theneedle electrode 126 can have a porous structure that allows infusaid toexit out through the pores. Further details regarding the manufactureand functionality of porous structures in ablation probes are disclosedin application Ser. No. 10/740,692 filed Dec. 18, 2003, now U.S. Pat.No. 7,347,859, and which is expressly incorporated herein by reference.When using side ports or porous structures, the needle electrode 126 canhave a closed-ended point, thereby facilitating introduction of theneedle electrode 126 through the tissue along a straight line.

The ablation probe 110 further comprises a temperature sensor 127, suchas a thermistor or thermocouple, mounted in the needle electrode 126.Signal wires (not shown) proximally extend from the temperature sensor127 back through the probe shaft 120. The temperature sensor 127 isdesigned to measure the temperature of the tissue at any given time,thereby providing an indication of whether or not infusaid should beperfused into the tissue. That is, if the tissue temperature isrelatively high, there is a danger that tissue charring may beoccurring, resulting in premature increasing of local tissue impedance.At this point, the conductivity of the tissue should be increased byinitiating or increasing perfusion of the infusaid into the tissue,thereby reducing the potential for tissue charring and prematureimpedance increase. If, on the other hand, the tissue temperature isrelatively low, there is no danger of charring the tissue, in whichcase, tissue perfusion is not immediately needed. Continuous perfusionof infusaid, however, would create a danger that the tissue will becomeflooded with the infusaid, thereby reducing predictability of theablation. As a practical example, the tissue temperature will dropbetween ablations when the tissue is not being actively ablated, inwhich case, continual perfusion is not desired. At this point, perfusionof the infusaid should be decreased or stopped.

Alternatively or optionally, an impedance sensor may be used to measurethe impedance of the tissue at any given time. Preferably, the needleelectrode 126 acts as the impedance sensor, which will complete anelectrical circuit with an external grounding electrode in order toprovide measurements of the tissue impedance. In a similar manner astissue temperature, tissue impedance provides an indication of whetheror not infusaid should be perfused into the tissue. That is, arelatively high tissue impedance indicates that the tissue may becharring, at which point perfusion of infusaid is desired. A relativelylow impedance indicates that there is no danger of tissue charring, atwhich point perfusion of infusaid is not desired.

Referring back to FIG. 3, the ablation probe 110 further comprises aconnector assembly 136 mounted on the proximal shaft end 122. Theconnector assembly 136 comprises a housing 138, a perfusion inlet port140, such as a male luer connector, mounted to the proximal end of thehousing 138, and a RF/signal port 142 mounted to the side of the housing138. The perfusion inlet port 140 is in fluid communication with theperfusion lumen 128 of the probe shaft 120 via an internal conduit (notshown) within the housing 138, and the RF/signal port 142 is inelectrical communication with the needle electrode 126 via the probeshaft wall 130, which extends into the housing 138. The RF/signal port142 is also in electrical communication with the temperature sensor 127(or alternatively an impedance sensor) via signal wires (not shown)extending through the probe shaft 120. The connector assembly 136 isalso provided with a nut 144, which engages the threads (not shown) ofthe cannula 108 in order to integrate the probe assembly 102 once theneedle electrode 126 is properly located at the target ablation site.The connector assembly 136 can be composed of any suitable rigidmaterial, such as, e.g., metal, plastic, or the like.

If the cannula 108 is not used, or if the cannula 108 is composed of anelectrically conductive material, the ablation probe 110 may comprise anoptional insulative sleeve 146 (illustrated in FIG. 4) that is disposedaround the entire length of the probe shaft 120, leaving the needleelectrode 126 exposed. The sleeve 146 can be formed around the probeshaft 120 in any one of a variety of manners, e.g., by co-extruding itover the probe shaft 120. If the cannula 108 is not used, or if thecannula 108 is composed of an electrically conductive material, thesleeve 146 is preferably composed of an electrically insulativematerial, such as plastic. In this manner, the RF energy conveyedthrough the probe shaft 120 will be concentrated at the target ablationsite adjacent the needle electrode 126.

Referring back to FIG. 1, the RF generator 104 is electrically connectedto the RF port 142 of the connector assembly 136 via an RF/signal cable148, which as previously described, is indirectly electrically coupledto the needle electrode 126 through the probe shaft 120, and indirectlycoupled to the temperature sensor 127 (or the impedance sensing element)via signal wires. The RF generator 104 is a conventional RF power supplythat operates at a frequency in the range from 200 KHz to 1.25 MHz, witha conventional sinusoidal or non-sinusoidal wave form. Such powersupplies are available from many commercial suppliers, such asValleylab, Aspen, and Bovie. Most general purpose electrosurgical powersupplies, however, operate at higher voltages and powers than wouldnormally be necessary or suitable for tissue ablation. Thus, such powersupplies would usually be operated at the lower ends of their voltageand power capabilities. More suitable power supplies will be capable ofsupplying an ablation current at a relatively low voltage, typicallybelow 150V (peak-to-peak), usually being from 50V to 100V. The powerwill usually be from 20 W to 200 W, usually having a sine wave form,although other wave forms would also be acceptable. Power suppliescapable of operating within these ranges are available from commercialvendors, such as Boston Scientific Corporation of San Jose, Calif., whomarkets these power supplies under the trademarks RF2000™ (100 W) andRF3000™ (200 W).

RF current is preferably delivered from the RF generator 104 to theneedle electrode 126 in a monopolar fashion, which means that currentwill pass from the needle electrode 126, which is configured toconcentrate the energy flux in order to have an injurious effect on thesurrounding tissue, and a dispersive electrode (not shown), which islocated remotely from the needle electrode 126 and has a sufficientlylarge area (typically 130 cm² for an adult), so that the current densityis low and non-injurious to surrounding tissue. In the illustratedembodiment, the dispersive electrode may be attached externally to thepatient, e.g., using a contact pad placed on the patient's flank. If theneedle electrode 126 is used as an impedance sensor, the dispersiveelectrode will be used to connect the circuit from the tissue back tothe RF generator 104.

The pump assembly 106 comprises a power head 150 and a syringe 152 thatis front-loaded on the power head 150 and is of a suitable size, e.g.,200 ml. The power head 150 and the syringe 152 are conventional and canbe of the type described in U.S. Pat. No. 5,279,569 and supplied byLiebel-Flarsheim Company of Cincinnati, Ohio. The pump assembly 106further comprises a source reservoir 154 for supplying the infusaid tothe syringe 152. The infusaid can be optionally cooled to provide theadditional beneficial effect of cooling the needle electrode 126 and thesurrounding tissue during the ablation process. The pump assembly 106further comprises a tube set 156 removably secured to an outlet 158 ofthe syringe 152. Specifically, a dual check valve 160 is provided withfirst and second legs 162 and 164, of which the first leg 162 serves asa liquid inlet connected by tubing 166 to the source reservoir 154. Thesecond leg 164 is an outlet leg and is connected by tubing 168 to theperfusion inlet port 140 on the connector assembly 136.

Thus, it can be appreciated that the pump assembly 106 can be operatedto periodically fill the syringe 152 with the infusaid from the sourcereservoir 154 via the tubing 166, and convey the infusaid from thesyringe 152, through the tubing 168, and into the perfusion inlet port140 on the connector assembly 136. The infusaid is then conveyed throughthe perfusion lumen 128 of the probe shaft 120, and out through theneedle electrode 126.

Other types of pump assemblies are also available for pumping infusaidthrough the probe shaft 120. For example, a saline bag can simply beconnected to the perfusion inlet port 140 on the connector assembly 136via tubing, and then raised above the patient a sufficient height toprovide the head pressure necessary to convey the infusaid through theprobe shaft 120 and out of the needle electrode 126. Alternatively, pumpassemblies can be conveniently incorporated within the connectorassembly 136, as described in further detail below.

The perfusion controller 107 is functionally coupled between the powerhead 150 of the pump assembly 106 and the temperature sensor 127. In theillustrated embodiment, the perfusion controller 107 is a stand-alonedevice that is coupled to the temperature sensor 127 through the RFgenerator 104 via a cable 109. Specifically, the perfusion controller107 is coupled to the RF generator 104 to obtain temperature feedbacksignals from the temperature sensor 127. Alternatively, the perfusioncontroller 107 can be incorporated into the RF generator 104, in whichcase, the cable 109 is not required. The perfusion controller 107 canalso be incorporated into the pump assembly 106. The RF generator 104,pump assembly 106, and perfusion controller 107 can even be incorporatedinto a single device similar to that disclosed in U.S. Pat. No.6,235,022, which is hereby fully and expressly incorporated herein byreference. A commercial embodiment of such an assembly (absent theperfusion feedback aspects) is marketed as the Model 8004 RF generatorand Pump System by Boston Scientific Corporation, located in San Jose,Calif. The Model 8004 RF generator need only be modified to incorporatethe perfusion controller 107 described herein.

In any event, the perfusion controller 107 turns the power head 150 onwhen the tissue temperature, as indicated by the temperature feedbacksignals received from the temperature sensor 127, surpasses an uppertemperature threshold. As a result, the power head 150 will operate thesyringe 152 in order to perfuse the infusaid through the tubing assembly156 and into the perfusion inlet port 140 of the ablation probe 110. Theinfusaid then travels down the perfusion lumen 128 of the ablation probe110, and out through the perfusion exit port 129 into the tissue. Theconductivity of the tissue will then increase, thereby providing for amore efficient and effective ablation process. When the tissuetemperature drops below a lower temperature threshold, indicating thatthere is too much infusaid within the tissue or the ablation process hastemporarily or permanently ceases, the perfusion controller 107 willturn the power head 150 off, thereby preventing further perfusion of theinfusaid until the tissue temperature surpasses the upper temperaturethreshold again.

The lower temperature threshold should be set at a level that is not soclose to the upper threshold level that the power head 150 will berapidly turned on and off during the ablation process, but should not beset so far from the upper threshold level that a wide tissue temperaturevariance is created. Alternatively, instead of using a lower temperaturethreshold, the perfusion controller 107 may turn the power head 150 onfor a predetermined period of time, after which the power head 150 isturned off until the tissue temperature surpasses the upper temperaturethreshold.

In an alternative embodiment, the feedback control system can beoverridden by providing a switch (not shown) on the pump assembly 106that can be manually operated by a physician. In this case, the switchcan be alternately operated to turn the power head 150 on and off at thediscretion of the physician. For example, the physician may desire toperfuse infusaid within the tissue prior to initiating the ablationprocess, or otherwise desire to increase or reduce the amount ofinfusaid perfuse regardless of the nature of the temperature feedbacksignals.

Referring now to FIGS. 5 and 6, an alternative embodiment of a probeassembly 202, which can be used in the tissue treatment system 100, willnow be described. The probe assembly 202 generally comprises anelongated cannula 208 and an inner probe 210 slidably disposed withinthe cannula 208. The cannula 208 has a proximal end 212, a distal end214, and a perfusion lumen (not shown) extending through the cannula 208between the proximal end 212 and the distal end 214. An open taperedpoint 218 is formed at the distal end 214 of the cannula 208 in order tofacilitate introduction of the cannula 208 through tissue. As with thecannula 108, the cannula 208 serves to deliver the active portion of theinner probe 210 to the target tissue, and may be rigid, semi-rigid, orflexible depending upon the designed means for introducing the cannula108 to the target tissue. The cannula 208 may have the same materialcomposition and dimensions as the cannula 108.

The inner probe 210 comprises a reciprocating shaft 220 having aproximal end 222 and a distal end 224 (shown in FIG. 5); a perfusionlumen (not shown) extending through the shaft 220 between the proximalend 222 and distal end 224; a cylindrical interface 228 mounted to thedistal end 224 of the shaft 220; and an array 230 of tissue penetratingneedle electrodes 232 mounted within the cylindrical interface 228. Theshaft 220 is slidably disposed within the perfusion lumen of the cannula208, such that longitudinal translation of the shaft 220 in a distaldirection 234 deploys the electrode array 226 from the distal end 214 ofthe cannula 208 (FIG. 6), and longitudinal translation of the shaft 218in a proximal direction 236 retracts the electrode array 226 into thedistal end 214 of the cannula 108 (FIG. 5).

Preferably, each of the needle electrodes 232 (or a subset thereof)comprises a lumen (not shown) that terminates in a perfusion exit port(not shown) and that is in fluid communication with the perfusion lumenwithin the shaft 220. In this manner, each of the needle electrodes 232is capable of perfusing the infusaid into the tissue. Alternatively, oroptionally, the cylindrical interface 228 or the probe shaft 220,itself, can have a perfusion exit port. Thus, like the ablation probe110, infusaid may flow through the perfusion lumen of the shaft 220,through the respective lumens of the needle electrodes 232 and out theexit ports. Alternatively, the needle electrodes 232 and/or the probeshaft 220 can have a porous structure.

Like the previously described probe 110, the probe 210 comprises atemperature sensor (not shown), which is mounted at the base of theneedle electrodes 232, preferably adjacent the cylindrical interface228. Alternatively, or optionally, the needle electrodes 232 can act asan impedance sensor. Signal wires (not shown) proximally extend from thetemperature sensor (or needle electrodes 232 if used as impedancesensors) back through the probe shaft 220.

The probe assembly 202 further comprises a connector assembly 238, whichincludes a connector sleeve 240 mounted to the proximal end 212 of thecannula 208 and a connector member 242 slidably engaged with the sleeve240 and mounted to the proximal end 222 of the shaft 220. The connectormember 242 comprises a perfusion inlet port 240 and a RF/signal port 246in which the proximal ends of the needle electrodes 230 (oralternatively, intermediate conductors) extending through the shaft 220of the inner probe 210 are coupled. The signal wires from thetemperature sensor 127 are also coupled to the RF/signal port 246. Theconnector assembly 238 can be composed of any suitable rigid material,such as, e.g., metal, plastic, or the like.

RF current can be delivered to the electrode array 230 in a monopolarfashion, as previously described above, or in a bipolar fashion, whichmeans that current will pass between “positive” and “negative”electrodes 232 within the array 230. In a bipolar arrangement, thepositive and negative needle electrodes 232 will be insulated from eachother in any regions where they would or could be in contact with eachother during the power delivery phase.

Further details regarding needle electrode array-type probe arrangementsare disclosed in U.S. Pat. No. 6,379,353, which is hereby expresslyincorporated herein by reference.

Having described the structure of the tissue treatment system 100, itsoperation in treating targeted tissue will now be described. Thetreatment region may be located anywhere in the body where hyperthermicexposure may be beneficial. Most commonly, the treatment region willcomprise a solid tumor within an organ of the body, such as the liver,kidney, pancreas, breast, prostrate (not accessed via the urethra), andthe like. The volume to be treated will depend on the size of the tumoror other lesion, typically having a total volume from 1 cm³ to 150 cm³,and often from 2 cm³ to 35 cm³. The peripheral dimensions of thetreatment region may be regular, e.g., spherical or ellipsoidal, butwill more usually be irregular. The treatment region may be identifiedusing conventional imaging techniques capable of elucidating a targettissue, e.g., tumor tissue, such as ultrasonic scanning, magneticresonance imaging (MRI), computer-assisted tomography (CAT),fluoroscopy, nuclear scanning (using radiolabeled tumor-specificprobes), and the like. Preferred is the use of high resolutionultrasound of the tumor or other lesion being treated, eitherintraoperatively or externally.

Referring now to FIGS. 7A-7C, the operation of the tissue treatmentsystem 100 is described in treating a treatment region TR within tissueT located beneath the skin or an organ surface S of a patient. The probeassembly 102 is described in this operation, although the probe assembly202 can be alternatively used. The cannula 108 is first introducedthrough the tissue T, so that the distal end 114 of the cannula 108 islocated at the treatment region TR, as shown in FIG. 7A. This can beaccomplished using any one of a variety of techniques. In a preferredmethod, the cannula 108 and probe 110 are introduced to the treatmentregion TR percutaneously directly through the patient's skin or throughan open surgical incision. In this case, the sharpened tip 118 of thecannula 108 facilitates introduction to the treatment region TR. In suchcases, it is desirable that the cannula 108 or needle be sufficientlyrigid, i.e., have a sufficient column strength, so that it can beaccurately advanced through tissue T. In other cases, the cannula 108may be introduced using an internal stylet that is subsequentlyexchanged for the ablation probe 110. In this latter case, the cannula108 can be relatively flexible, since the initial column strength willbe provided by the stylet. More alternatively, a component or elementmay be provided for introducing the cannula 108 to the target ablationsite TS. For example, a conventional sheath and sharpened obturator(stylet) assembly can be used to initially access the tissue T. Theassembly can be positioned under ultrasonic or other conventionalimaging, with the obturator/stylet then removed to leave an access lumenthrough the sheath. The cannula 108 and probe 110 can then be introducedthrough the sheath lumen, so that the distal end 114 of the cannula 108advances from the sheath into the target ablation site TS.

After the cannula 108 is properly placed, the probe shaft 120 isdistally advanced through the cannula 108 to deploy the needle electrode126 out from the distal end 114 of the cannula 108, as shown in FIG. 7B.Once the cannula 108 and probe 110 are properly positioned, the ablationprobe 110 and cannula 108 can then be integrated with each other bythreading the nut 144 around the threaded portion of the cannulaproximal end 112. The RF generator 104 is then connected to theconnector assembly 136 via the RF port 142, and the pump assembly 106 isconnected to the connector assembly 136 via the perfusion inlet port140. The RF generator 104 is then operated to ablate the treatmentregion TR, and the pump assembly 106, under control of the perfusioncontroller 107, is operated to perfuse the treatment region TR withinfusaid when necessary, i.e., when the tissue temperature is above theupper temperature threshold. As a result, lesion L will be created, asillustrated in FIG. 7C, which will eventually expand to include theentire treatment region TR.

Although the pump assembly 106 has been described as being external tothe ablation probe 110, a pump can alternatively be incorporated into anablation probe. Such a feature obviates the need to set up and connectthe pump assembly to the ablation probe, thereby simplifying theablation process. Turning to FIG. 8, an ablation probe 310 with anincorporated pump will now be described. The ablation probe 310 issimilar to the previously described ablation probe 110, with theexception that the ablation probe 310 includes a connector assembly 336with a pump assembly 306. The connector assembly 336 comprises a housing338 in which the pump assembly 306 is mounted.

The pump assembly 306 is powered and controlled by the perfusioncontroller 107, which can be either be located within the RF generator104 or can be a stand-alone device. If room permits, the perfusioncontroller 107 can even be incorporated within the connector assembly336—perhaps as another component of the pump assembly 306. The connectorassembly 336 comprises a perfusion control port 342 mounted to theexterior of the housing 338. The perfusion controller 107 iselectrically coupled to the pump assembly 306 via a power/signal cable340, which mates with the perfusion control port 342. Alternatively, ifthe perfusion controller 107 is incorporated into the RF generator 104,the perfusion controller 107 can be connected to the pump assembly 306via the RF/signal port 142, in which case, a separate cable 340 andperfusion control port 342 is not needed. Thus, the perfusion controller107 may supply power to the pump assembly 306 and alternately turn thepump assembly 306 on and off by transmitting control signals to the pumpassembly 306.

The connector assembly 336 further comprises a perfusion inlet port 340mounted to the exterior of the housing 338. The perfusion inlet port 340is in fluid communication with the pump assembly 306. A source ofinfusaid 346, such as a saline bag, is in fluid communication with theperfusion inlet port 340 via tubing 348. Thus, the pump assembly 306 canbe operated to pump the infusaid supplied by the infusaid source 346into the perfusion lumen 128 of the ablation probe 310.

Turning now to FIG. 9, the pump assembly 306 will now be described infurther detail. The pump assembly 306 comprises a reservoir 350 thatstores the infusaid received from the infusaid source 346. In theillustrated embodiment, the active component of the pump assembly 306 isbased on piezoelectric transducer technology. Specifically, the pumpassembly 306 comprises a diaphragm 352 that encloses the proximal sideof the reservoir 350. The diaphragm 352 is composed of an elastomericmaterial, e.g., a polymeric substance, such that the diaphragm 352 canalternatively move toward and away from the reservoir 350 in an elasticmanner. The pump assembly 306 further comprises a piezoelectric element354 suitably bonded to the proximal side of the diaphragm 352, and anelectronic circuit 356 that is electrically coupled to electrodes (notshown) on the piezoelectric element 354. Under control of the perfusioncontroller 107, the electronic circuit 356 transmits electrical currentto the piezoelectric element 354 at a high frequency, which causes thepiezoelectric element 354 to vibrate towards (the pumping stroke) andaway from (the return stroke) the infusaid stored in the reservoir 350.

Thus, during the pumping stroke, the diaphragm 352 moves into thereservoir 350, causing the pressure within the reservoir 350 toincrease. As a result, a portion of the infusaid is displaced from thereservoir 350 into the perfusion lumen 128. A one-way check valve 358 isprovided between the perfusion inlet port 140 and the reservoir 350 toprevent the infusaid in the reservoir 350 from being displaced backthrough the perfusion inlet port 140 and into the infusaid source 346.During the return stroke, the diaphragm 352 moves away from thereservoir 350, causing the pressure within the reservoir 350 todecrease. As a result, a portion of the infusaid within the infusaidsource 346 is forced (sucked) into the reservoir 350. Another one-waycheck valve 360 is provided between the perfusion lumen 128 and thereservoir 350 to prevent the infusaid within the perfusion lumen 128from being forced (sucked) back into the reservoir 350. Similar types ofpiezoelectric activated devices are marketed as fluid atomizers by APCInternational, Ltd., located in Mackeyville, Pa.

The pump assembly 306 can also be incorporated into a multi-electrodeablation probe similar to that illustrated in FIGS. 5 and 6. In thiscase, the pump assembly 306 may be incorporated into the connectormember 242. The ablation probe 310 can be used with the cannula 108 andthe RF generator 104 to ablate and perfuse tissue in the same mannerdescribed above with respect to FIGS. 7A-7C. The main difference is thatan external pump assembly need not be set up and connected to theablation probe 310. Rather, only the infusaid source 346 need only beconnected to ablation probe 310.

Although the previously described perfusion controller 107 has beendescribed as controlling the perfusion of the infusaid by controllingthe operation of the pump assemblies 106 and 306, a perfusioncontroller, which takes the form of a valve, can instead be used tocontrol the perfusion downstream from the pump assemblies 106 and 306.Specifically, and with reference to FIGS. 10-13, an ablation probe 410that implements this concept will now be described. The ablation probe410 is similar to the previously described ablation probes 110 and 310,with the exception that the distal end 124 of the probe shaft 120comprises a perfusion control valve 407 that controls the amount ofinfusaid perfused into the tissue. The ablation probe 410 may operatewith the RF generator 104 and the external pump assembly 106 illustratedin FIG. 1, or alternatively, the pump assembly 306 illustrated in FIGS.8 and 9 can be incorporated into the proximal end of the ablation probe410. Because direct control is exercised over the pump assembly, theablation probe 410 may alternatively incorporate various types ofmanually activated pump assemblies within its proximal end, as will bedescribed in further detail below.

In the illustrated embodiment, the control valve 407 takes the form of areed valve that comprises four reeds 452 and a perfusion exit port 429(shown in FIGS. 12 and 13). The reeds 452 are designed to collapse uponeach other in the presence of a relatively low tissue temperature (FIGS.10 and 11), and move away from other in the presence of a relativelyhigh temperature (FIGS. 12 and 13). When fully collapsed, the reeds 452form a tissue penetrating point 426 that facilitates introduction of theablation probe 410 through tissue. Notably, the control valve 407 willonly be exposed to body temperature during its introduction through thetissue, and thus, the reeds 452 will be fully collapsed in order to formthe point 426. During the ablation process, the control valve 407 willopen, at which point the tissue penetrating tip 426 will not exist.Because the ablation probe 410 will presumably be stabilized during theablation process, however, the tissue penetrating tip 426 is not needed.

Referring now to FIGS. 14 and 15, each of the reeds 452 is composed of abi-metallic flange, so that the reeds 452 collapse towards each otherand move away from either in the presence of temperature changes. Thatis, each reed 452 comprises an outer layer of metal 454 having aspecific coefficient of thermal expansion (CTE) and an inner layer ofmetal 456 having a higher CTE. For example, the outer layer 454 can becomposed of gold, which has a CTE of 7.9×10⁻⁶/° F. and the inner layer456 can be composed of copper, which has a CTE of 9.2×10⁻⁶/° F.

Thus, when the tissue temperature increases, the inner layer 456 willexpand along the length of the reed 452 at a rate that is greater thanthe rate that the outer layer 454 expands along the length of the reed452. As a result, each reed 452 will deform outward, thereby increasingthe size of the perfusion exit port 429, which, in turn, increases theamount of infusaid that is perfused out of the ablation probe 410. Eachreed 452 will stop deforming outward until the temperature reaches astead-state—preferably below 100° C. In contrast, when the tissuetemperature decreases, the inner layer 456 will contract along thelength of the reed 452 at a rate that is greater than the rate that theouter layer 454 contracts along the length of the reed 452. As a result,each reed 452 will deform inward, thereby decreasing the size of theperfusion exit port 429, which, in turn, decreases the amount ofinfusaid that is perfused out of the ablation probe 410. Each reed 452will stop deforming inward until either the temperature reaches astead-state or the reeds 452 have fully collapsed upon each other,whichever happens first. Preferably, the perfusion exit port 429 iscompletely closed when the reeds 452 are in the fully collapsed state,so that no infusaid can be perfused out of the ablation probe 410 atthis point.

It should be noted that there are other ways in which the reeds 452 candeform in the presence of tissue temperature change. For example, thereeds 452 may be composed of nitinol, which is preferably shaped andprocessed, such that the reeds 452 deform outward when the tissuetemperature increases, and curved inward when the tissue temperaturedecreases. The manufacture and functionality of nitinol flangesexhibiting these properties is well known in the art and will thus notbe discussed in further detail. Thus, like a bi-metallic reed, when thetemperature increases, each reed 452 will deform outward, which, inturn, increases the amount of infusaid that is perfused from theablation probe 410. When the temperature decreases, each reed 452 willdeform inward, which, in turn, decreases the amount of infusaid that isperfused from the ablation probe 410.

The ablation probe 410 further comprises an electrode, which can eitherbe carried by, or integrated in, the reeds 452 of the control valve 407.For example, a conductive element (not shown) can be applied to eachreed 452, with each conductive element forming a portion of theelectrode, or the outer layer 454 of each reed 452 (in the case of abi-metallic reed 452) can function as a portion of the electrode. Theoutside of the reeds 452 can optionally be faceted in order tofacilitate visualization of the electrode during fluoroscopy.

As briefly discussed above, manually activated pump assemblies canalternatively be incorporated into the proximal end of the ablationprobe 410. For example, FIG. 16 illustrates the proximal end of theablation probe 410, which includes a connector assembly 436 that issimilar to the previously described connector assembly 336, with theexception that it includes a manually activated pump assembly 406. Theconnector assembly 436 comprises a housing 438 in which the pumpassembly 406 is mounted. The connector assembly 436 further comprisesthe previously described RF port 142 to which the RF generator 104 canbe connected, and a perfusion inlet port 440 mounted to the exterior ofthe housing 438. The perfusion inlet port 440 is in fluid communicationwith the pump assembly 406. A source of infusaid 446, such as syringe,can be used to inject infusaid into the connector assembly 436 via theperfusion inlet port 440. Thus, the pump assembly 406 can be operated-topump the infusaid supplied by the infusaid source 446 into the perfusionlumen 128 of the ablation probe 410.

In performing its function, the pump assembly 406 comprises a reservoir450 that stores the infusaid received from the infusaid source 446, anda diaphragm 452 that encloses the proximal side of the reservoir 450.Thus, when the syringe 152 conveys infusaid through the perfusion inletport 440 and into the reservoir 450 under positive pressure, thediaphragm 452 will expand from its fully contracted position towards theproximal end of the housing 438 in order to accommodate the infusaidreservoir 450, as shown in phantom in FIG. 16. Once the diaphragm 452 isforced against the proximal end of the connector housing 438, thereservoir 450 will be completely filled with infusaid, and the reservoir450 will, in turn, be fully pressurized. A one-way check valve 458 isprovided within the perfusion inlet port 440 to prevent the infusaidfrom escaping once the syringe 446 is removed from the perfusion inletport 440. Alternatively, the syringe 446 can be left in place during theablation process, in which case, a one-way check valve may not beneeded.

Notably, the control valve 407 at the proximal end of the ablation probe410 will be exposed to room temperature during the filling process, inwhich case, the perfusion exit port 429 will be totally closed at roomtemperature, thereby preventing infusaid from escaping the ablationprobe 410 as the reservoir 450 is being filled. During the ablationprocess, the control valve 407 will be exposed to high temperatures, inwhich case, the perfusion exit port 429 will open, with the size of theopening depending upon the immediate tissue temperature. At this point,the infusaid, which is under positive pressure, will be forced out ofthe reservoir 450, through the perfusion lumen 128, and out of theperfusion exit port 429 into the tissue. As infusaid is forced out ofthe reservoir 450, the diaphragm 452 will contract, thereby maintainingpositive pressure within the reservoir 450. Once the diaphragm 452returns to its fully contracted state, the reservoir 450 will no longerbe pressurized, in which case, the infusaid will not be forced out ofthe reservoir 450, and perfusion ceases. If the ablation process has notbeen terminated, the reservoir 450 can be filled with more infusaid inorder to pressurize the reservoir 450 and perfusion of the infusaid canagain be commenced should it be necessary.

The ablation probe 410 can be used with the cannula 108 and the RFgenerator 104 to ablate and perfuse tissue in the same manner describedabove with respect to FIGS. 7A-7C. The main difference is that neitheran external pump assembly nor a pump controller needs to be set up andconnected to the ablation probe 410. Rather, only the infusaid source346 need only be connected to ablation probe 410.

FIGS. 17 and 18 illustrate another connector assembly 536 that can bemounted to the proximal end of the ablation probe 410. The connectorassembly 536 comprises the previously described RF port 142 to which theRF generator 104 can be connected, and a perfusion inlet port 540 towhich a source of infusaid 346, such as a saline bag, can be connectedvia the tube 348 (shown in FIG. 8). The connector assembly 536 furthercomprises a manually activated pump assembly 506, which comprises areservoir 550 and a plunger 552.

Specifically, the plunger 552 comprises a plunger head 554, whichdivides the reservoir 350 into proximal and distal reservoir regions 560and 562. The plunger head 554 comprises a seal 564 that interfaces withthe inner surface of the housing 538, such that the proximal and distalreservoir regions 560 and 562 are completely sealed from each other. Thecross-section of the plunger head 554 and reservoir 550 are preferablycircular, but can be other shapes as well, as long as a sufficient sealis created between the plunger head 554 and the inside surface of thehousing 538.

The plunger 552 further comprises a plunger shaft 556, the distal end ofwhich is mounted within the plunger head 554, and the proximal end ofwhich extends out an opening 566 within the proximal end of the housing538. A handle 568 is formed at the proximal end of the plunger shaft552, so that a physician can pull the plunger 552 in the proximaldirection by a physician, as illustrated in FIG. 15. As a result of theproximal displacement of the plunger head 554, the pressure within thedistal reservoir region 562 decreases, and a portion of the infusaidwithin the infusaid source 346 is forced (sucked) into the distalreservoir region 562. Thus, when the plunger 552 is pulled to its mostproximal position, the reservoir 550 will be completely filled withinfusaid.

The pump assembly 506 further comprises a spring 570 disposed betweenthe plunger head 554 and the proximal end of the housing 538. Thus, oncethe plunger handle 568 is released, the spring 570 will urge the plungerhead 554 in the distal direction, thereby pressurizing the reservoir550. A one-way check valve 558 is provided between the perfusion inletport 540 and the reservoir 550 to prevent the infusaid in the reservoir550 from being displaced back through the perfusion inlet port 540 andinto the infusaid source 346.

Since the control valve 407 will be exposed to room temperature duringthe filling process, the perfusion exit port 429 will be totally closedat room temperature, thereby preventing infusaid from escaping out ofthe distal end of the ablation probe 410 when the plunger handle 568 isreleased. Optionally, the plunger 552 can include a locking mechanism(not shown) that locks the plunger 552 in placed once it is pulled backto its most proximal position. During the ablation process, the controlvalve 407 will be exposed to high temperatures, in which case, theperfusion exit port 429 will open. At this point, the infusaid, which isunder positive pressure, will be forced out of the reservoir 550,through the perfusion lumen 128, and out of the perfusion exit port 429into the tissue. As infusaid is forced out of the reservoir 350, thespring 570 will force the plunger head 554 to move in the distaldirection, thereby maintaining positive pressure within the reservoir550. Once the spring 570 returns to its uncompressed position, theplunger head 554 will stop moving, the reservoir 550 will no longer bepressurized, in which case, the infusaid will not be forced out of thereservoir 550, and perfusion ceases. If the ablation process has notbeen terminated, the plunger shaft 556 can be pulled back to fill thereservoir 550 with more infusaid, and then released in order topressurize the reservoir 550 and commence perfusion of the infusaidagain should it be necessary.

Referring now to FIG. 19, another ablation probe 610 that can be usedwith the RF generator 104 and any of the previously described pumpassemblies will be described. The ablation probe 610 is similar to thepreviously described ablation probe 110, with the exception that theablation probe 610 comprises a wicking material 650 disposed within theperfusion lumen 128. The wicking material 650 can be composed of anymaterial that exhibits capillary action (e.g., cotton or fabric). Inthis manner, the wicking material 650 serves to regulate the flow ofinfusaid through the perfusion lumen 128.

Significantly, because the infusaid will travel through the perfusionlumen 128 in a slow and controlled manner due to the capillary action ofthe wicking material 650, the size of the perfusion exit ports at thedistal end 124 of the shaft 120 can be made much larger, therebypreventing or minimizing clogging of the perfusion exit ports. In theillustrated embodiment, the ablation probe 610 is provided withrelatively large side perfusion exit ports 629 out which the infusaidwill seep from the wicking material 650. Because the infusaid will beperfused out of the side perfusion exit ports 629, the ablation probe610 is provided with a close-ended needle electrode 626, therebyfacilitating introduction of the shaft 120 through the tissue along astraight line. Alternatively or optionally, the previously describedtapered needle electrode 126 can be provided.

In the case of ablation probes with needle electrode arrays, such as theablation probe 210 illustrated in FIGS. 5 and 6, the wicking materialcan also be disposed within the lumens running through the needleelectrodes, as well as the perfusion lumen extending through the shaft.

Any of the previously described pump assemblies, including a raisedsaline bag, can be used to pump the infusaid through the perfusion lumen128. The ablation probe 610 can be used with the cannula 108 and the RFgenerator 104 to ablate and perfuse tissue in the same manner describedabove with respect to FIGS. 7A-7C. The main difference is that cloggingof the perfusion exit ports will not be a significant concern whenintroducing the ablation probe 610 through the tissue.

Although particular embodiments of the inventions have been shown anddescribed herein, there is no intention to the present inventions to thedisclosed embodiments. Indeed, and it will be apparent to those skilledin the art that various changes and modifications may be made withoutdeparting from the scope of the inventions, as recited in the followingclaims.

What is claimed is:
 1. An ablation probe, comprising: an elongate shafthaving a proximal end and a distal end, wherein the distal end comprisesa sharpened, open-ended, tapered tip ablative element; a perfusion lumenlongitudinally extending within the shaft; at least one perfusion exitport in fluid communication with the perfusion lumen: a connectorassembly, the connector assembly comprising a housing having a proximalend and a distal end, wherein the distal end of the housing comprises athreaded nut directly coupled to the proximal end of the shaft; a pumpassembly disposed within the housing of the connector assembly, the pumpassembly configured for pumping infusaid through the perfusion lumen andout the at least one perfusion exit port; a reservoir for storing theinfusaid of the pump assembly; and a perfusion inlet port configured fortransferring infusaid from an external source into the reservoir forstoring the infusaid of the pump assembly; wherein the pump assemblycomprises a plunger, the plunger having a pumping stroke that displacesthe infusaid from the reservoir into the perfusion lumen, and a returnstroke that displaces the infusaid from the external source into thereservoir; wherein the shaft is a unibody structure, and wherein theentire unibody structure is an electrically conductive material; andwherein the ablation probe is devoid of a secondary shaft that surroundsthe unibody structure of the shaft.
 2. The probe of claim 1, wherein theat least one perfusion exit port is disposed on a side of the perfusionlumen.
 3. The probe of claim 1, wherein the at least one perfusion exitport is carried by the ablative element.
 4. The probe of claim 1,wherein the pump assembly comprises a one-way check valve disposedbetween the perfusion inlet port and the reservoir.
 5. The probe ofclaim 4, wherein the one-way check valve prevents the infusaid in thereservoir from being displaced back through the perfusion inlet port andinto the external source.
 6. The probe of claim 1, wherein the plungercomprises a plunger head adjacent the reservoir, the plunger head havinga seal that interfaces with an internal surface of the housing of theconnector assembly.
 7. The probe of claim 6, wherein the plunger headcomprises a cross-section having a circular shape.
 8. The probe of claim6, wherein the plunger comprises a plunger shaft having a distal enddisposed on the plunger head, the plunger shaft further having aproximal end extending out an opening of the housing of the connectorassembly.
 9. The probe of claim 8, wherein the plunger comprises aplunger handle disposed on the proximal end of the plunger shaft. 10.The probe of claim 6, wherein the pump assembly comprises a springdisposed between the plunger head and the internal surface of thehousing of the connector assembly, the spring configured forpressurizing the reservoir.
 11. The probe of claim 1, wherein a side ofthe housing of the connector assembly comprises a radio frequency portin electrical communication with the ablative element.
 12. The probe ofclaim 1, wherein the perfusion inlet port is disposed on a side of thehousing of the connector assembly.
 13. The probe of claim 1, wherein theconnector assembly comprises a rigid metal material.